Comment by WickyNilliams

Fwiw I tried every tool imaginable a few years ago including kubb, (which I think I contributed to while testing things out)

The only mature, correct, fast option with a fixed cost (since it mostly exists at the type level meaning it doesn't scale your bundle with your API) was openapi-ts. I am not affiliated other than a previous happy user, though I did make some PRs while using it https://openapi-ts.dev/